1. (Field of the Invention)
This invention relates to an improvement in a structure of a thin DC brushless motor and, more particularly, to a bearing structure of a thin DC brushless motor.
2. (Description of the Prior Art)
A thin DC brushless motor has been frequently used as a rotary drive source of a floppy disk drive for a personal computer. FIG. 4 is a sectional view showing a conventional thin DC brushless motor illustrating the state that a rotor is rotatably provided on a motor mounting plate formed of a printed circuit board. In FIG. 4, numeral 1 denotes a board as a motor mounting plate, which is made of a ferromagnetic material such as steel and on which a printed wiring circuit is formed on the surface through a thin insulating layer, and an electronic component such as an IC for a motor drive circuit is mounted. A circular hole 2 is perforated at the board 1, a bearing base 3 is engaged within the circular hole 2, and clamped at the board with screws 4. Two ball bearings 5 and 6 are secured to the bearing base 3.
Numeral 7 designates a rotating disk for rotating the floppy disk to constitute a rotor in a thin circular dish shape. The rotating poles 9 made of a ringlike permanent magnet are fixed to the inside of the outer periphery 8 of the rotating disk 7. A speed detecting permanent magnet 10 for detecting the rotating speed of the rotating disk 7 is fixed to the lower part of the outer periphery 8 of the rotating disk 7. The poles 9 made of the permanent magnet are formed of rare earth metal or the like in a ring shape as shown in FIG. 5. A magnetic shielding plate 30 formed of soft iron similarly in a ring shape is engaged outside the poles 9. A plurality of permanent magnets is formed at the poles 9 by magnetizing. These permanent magnets are magnetized in the radial direction of the poles 9 in such a manner that the polarity directions of these poles are opposite at the adjacent poles. A rotating disk 7 assembly including the poles 9 constitutes a rotor.
A rotating shaft mounting plate 11 made of brass is fixed to the center of the rotating disk 7 and receives thereon circular member 24. A rotating shaft 12 is fixed to the center of the rotating shaft mounting plate 11. The rotating shaft 12 is rotatably mounted at the ball bearings 5 and 6. As also known in the art, reference numeral 13 denotes a hole receiving a driving pin 14 which chucks to a floppy disk and transmits a rotating force of the rotating disk 7 thereto. The numeral 15 is a leaf spring which biases the drive pin 14 upwardly and downwardly in accordance with loading of the floppy disk. The numeral 22 is a coil wound on the stator pole 21 to generate a magnetic pole. The numeral 25 is an electric terminal for an electric current flowing from the mounting plate 1 to the ground.
In a conventional thin DC brushless motor shown in FIGS. 4 and 5, the bearing base 3 for holding the ball bearings 5, 6 for rotatably supporting the rotating shaft 12 is constructed separately from a stator frame 23 having a stator core 31 and stator poles 21. However, such a thin DC brushless motor has been required to be reduced in size and thickness without decreasing its output in the development of a light, thin, short and small articles.
Therefore, to maintain the output of the conventional thin DC brushless motor in a smaller space, a gap G between the rotating poles 9 and the stator poles 21 is reduced to its critical limit. In this respect, the squareness of the rotating shaft 12 to the stator poles 21 becomes a problem. The squareness cannot be obtained in a stable accuracy maintained accurately since the stator poles 21 and the bearing base 3 for receiving the bearings 5, 6 are have been formed separately, and respectively fixed to the board 1.
This invention is constituted in view of the above-described circumstances, and an object of this invention is not only to facilitate the squareness management of the bearing mechanism for the stator poles 21 but also to reduce the cost by the decrease in the number of components.